Soils generally produce humic substances that are a source of percolating water acidity. The acidity is believed to be associated with the type of vegetation cover. The karst soils formed under coniferous in the Koňský Spád site (Moravian Karst) were studied to deduce a risk for karst/cave environment. The soils were classified as strongly acidic, based on the minimum of pH values of soil leachates (pH ~ 2.99 in KCl solution; pH ~ 3.82 in water). It was found that the soil acidity markedly exceeds the soil alkalinity and that the acidity of upper soils horizons exceeds the acidity of the lower horizons. The very low variability in the spatial distribution of acid-base parameters (pH, acidity, and alkalinity) indicates that a uniform type of vegetation produces nearly identical acid-base properties. The results showed that acidity of the soil under coniferous vegetation is responsible for a strong aggressiveness to underlying rocks. However, it seems evident that (i) the acidity is neutralized on the base of soil profile by reaction with limestone clasts and that (ii) the acidic solutions do not permeate deeper into vadose zone/caves.Soils generally produce humic substances that are a source of percolating water acidity. The acidity is believed to be associated with the type of vegetation cover. The karst soils formed under coniferous in the Koňský Spád site (Moravian Karst) were studied to deduce a risk for karst/cave environment. The soils were classified as strongly acidic, based on the minimum of pH values of soil leachates (pH ~ 2.99 in KCl solution; pH ~ 3.82 in water). It was found that the soil acidity markedly exceeds the soil alkalinity and that the acidity of upper soils horizons exceeds the acidity of the lower horizons. The very low variability in the spatial distribution of acid-base parameters (pH, acidity, and alkalinity) indicates that a uniform type of vegetation produces nearly identical acid-base properties. The results showed that acidity of the soil under coniferous vegetation is responsible for a strong aggressiveness to underlying rocks. However, it seems evident that (i) the acidity is neutralized on the base of soil profile by reaction with limestone clasts and that (ii) the acidic solutions do not permeate deeper into vadose zone/caves
